In the early 1940s, Dr. Papanicalou developed a technique whereby cells from the uterine cervix could be sampled with a cotton swab, placed on a glass slide, stained and examined for evidence of malignant change. The technique was named after him and has been referred to as the "PAP" smear. In the last fifty years the PAP smear has been used as a screening test for cancer. In addition, during the last fifteen years many refinements of this procedure have been developed, so that it is no longer used exclusively for cancer detection but is now also used to diagnose sexually transmitted diseases, to determine hormonal function, and to assess the possibility of threatened abortion. The accuracy of results obtained in a "PAP" smear is dependent on three variable: (1) the sample taken; (2) the laboratory procedure for processing and preparing the sample for interpretation; and (3) the accuracy of the interpretation of the prepared and processed sample. Of the three variables, errors in the sample taken appear to have the largest effect on the accuracy of results.
The collection of samples for PAP smears is usually done by a physician or a trained practitioner. The sample is taken through a speculum which is inserted into the vaginal opening. Samples are best taken from the transformation zone of the cervix. This zone is the area of change in the type of cells that line the cervix and this area most frequently reveals the development of cancer. Many methods for sampling the transformation zone have been devised. Current procedures employ cotton swabs, wood spatulas, and nylon brushes. However, these devices are less than fully satisfactory because they do not provide a fully representative sample of transformation zone cells.
Impression cytology is a procedure in which a filter is placed in contact with a tissue surface and then removed. When the filter is removed a thin layer of cells typically adheres to the filter. The filter and adherent cells are then processed and examined microscopically for diagnostic purposes. This technique has been used for diagnosis of a variety of eye conditions, such as blepharoconjunctivitis, keratoconjunctivitis sicca, and primary ocular surface disease. (Nelson, et al., Archives Ophthalmology, vol. 101, pp. 1869-1872, 1983.) The technique of impression cytology has also been applied to the examination of tissues which have been surgically removed, for example, cervical tumors and hysterectomy specimens, and biopsies. (Koprowska, et al., Acta Cytologica, vol. 30, pp. 207-212, 1986.) The present invention applies the technique of impression cytology to the sampling of cells from the human female reproductive tract.